1. Field of the Invention
The present invention relates to a cleaning method and a substrate processing apparatus, and in particular relates to a cleaning method for a substrate processing apparatus using plasma produced from a fluorocarbon-based process gas.
2. Description of the Related Art
A substrate processing apparatus that subjects a semiconductor wafer (hereinafter referred to merely as a “wafer”) as a substrate to plasma processing has an accommodating chamber in which a wafer is accommodated. A process gas is supplied to the interior of the accommodating chamber, and the supplied process gas is excited to be turned into plasma. Here, if a fluorocarbon-based (CF-based) gas is used, CF type deposit and hydrocarbon type (CH type) deposit become attached to surfaces of component parts and inner wall surfaces of the accommodating chamber. While the next wafer is being subjected to the plasma processing, the attached deposit may come off and turn into particles, and the particles may become attached to the wafer. Moreover, the attached deposit may become dissociated again to affect the characteristics of the plasma processing, for example, the characteristics of etching.
Accordingly, dry cleaning has conventionally been carried out so as to remove the CF type deposit and the CH type deposit attached to surfaces of component parts and so on in the accommodating chamber. In the dry cleaning, oxygen gas is supplied to the interior of the accommodating chamber, and the oxygen gas is excited to produce plasma. Oxygen radicals (O radicals and O2 radicals) in the plasma react with the CF type deposit and the CH type deposit and turn into carbon monoxide (CO) and carbon dioxide (CO2). The carbon monoxide and carbon dioxide are discharged from the accommodating chamber. As a result, the CF type deposit and the CH type deposit are removed.
To facilitate the removal of the CF type deposit and the CH type deposit, there has been known that not only oxygen gas but also carbon tetrafluoride (CF4) gas is supplied to the interior of the accommodating chamber (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. H11-145115). The carbon tetrafluoride gas is excited to produce fluorine radicals. The fluorine radicals tend to bind with carbon atoms, and hence facilitate decomposition of the CF type deposit and the CH type deposit.
In the substrate processing apparatus, a sealing member, in particular, an O-ring has been widely used so as to seal the interior of the accommodating chamber from outside.
However, the O-ring is made of fluorine-based rubber (for example, FKM), and the composition thereof is similar to the composition of the CF type deposit and the CH type deposit. For this reason, if carbon tetrafluoride gas is used in the dry cleaning, the O-ring may abnormally wear due to fluorine radicals produced from the tetrafluoride gas.
Moreover, even if carbon tetrafluoride gas is not used in the dry cleaning, fluorine radicals are produced at the same time when the CF type deposit attached to surfaces of component parts in the accommodating chamber react with oxygen radicals to produce carbon monoxide and carbon dioxide, and hence the O-ring may abnormally wear after all.